Tuning circuit



July 2, 1935. Bl TREVOR 2,006,526

TUNING CIRCUIT f Filed Feb. l2, 1952 -hllml N INVENTOR I BERTRAM TREVOR A BY 77%; A /I/z/'Tl/L- mo Niv-:Y

Patented July 2, 1935 UNITED STA-TES PATENT OFFICE TUNING CIRCUIT Bertram Trevor, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 12, 1932, serial No. 592,532

s claims. (o1. 179-171) This invention relates to radio signalling sysnew and efficient method of and means for pertems, and more in particular to a new and novel mitting ganging of the several tuned circuits. means for receiving signals. The above objects are attained by making the More in detail, my inventionrelates to receivtuning inductances following the inputl circuit ing means comprising a plurality of thermionic of a value higher than the inductance in the 5 tubes connected in cascade by tuned circuits so input circuit. When the inductances of all but that signals over a band of frequencies may be the first stage are increased sufliciently the paralireceived. The interconnecting circuits are conlel inductive reactance due to the choke inducttrolled in general by aplurality of tuning capaciance in the plate circuit will lower the effective 1o ties all connected to a single control means so inductance in the tuned circuit sufficiently to per-l I0 that the receiver may be tuned over the pre mit all of the condensers in the set to be gange'd.

determined range by a single operation. In these The novel features of my invention have been receivers known hereinbefore the initial inductpointed out with particularity in the claims apance in the input circuit of the first tube is coupended hereto. The nature of my invention and pled toa source of oscillations, as, for instance, the operation thereof will be understood from I6' an antenna system, While the output electrode the following detailed description thereof and of each thermionic tube is connected in two cirtherefrom when read in connection with the cuits, one of Which comprises a choking inductdrawing, in which the single figure illustrates ance" and a source of potential, and the other of one embodiment of the present invention.

2o which includes a stopping capacity and an in- Referring in particular to the drawing, A 20 ductance which is tuned by a variable capacity indicates an aerial system connected through a similar to the capacity tuning the initial inductcoupling inductance 2 to ground G. The receiver ance in the input circuit of the system. One terproper comprises thermionic tubes 4, 6 and 8 coin minal of each tuned inductance is connected to nected inv cascade as indicated. The control elec-'- the control electrode of a succeeding tube, while trode 3 of thermionic tube 4 is connected through 25 the other terminal of theinductance is connected tuning inductance L to the cathode I of tube 4. to the cathode of a succeeding tube. The input The control electrodes 9 and I3 of tubes 6 and electrodes of all of the following stages are con- 8 respectively are connected through inductances nected to the. output of the preceding stage by L1 and L2 to the cathodes II and I5 respectively.v

an arrangement similar tothe arrangementjust Direct current potential is supplied Jtothe anodesv l0 described, i I0 and I2 of tubes 4 and 6 respectively through In systems as described briefly above, and radio frequency choking inductances I, each of known'hereinbefore in the prior art, it has been which has one terminal connected to its'respecfound that, due to the fact that the choking intive anode and its other terminal connected to a ductance in the output circuit of one stage is in positive point on a source of potential indicated 85 eifectin parallel with the tuning inductance of at B-lof potential. The potential oscillations a following stage, whereas the initial induotance, signal frequency relayed in 4' and appearing that is, the tuning inductance connected'with the on It are impressed through blocking condensers input electrodes of the rst tube, is not so com BC on to the input circuit of tube 6 while the 40 nected, considerable difficulty has been cncountpotential oscillations at signal frequency relayed 40 ered in gauging the several tuning capacities so in 6 and appearing on I2 are vimpressed through that they keep in step over the entire tuning blocking condenser BC, on the input circuit of range. Especially is this true where the fretube 8. Any radio frequencies appearing inin quency of the signal received is well below the ductances I are shunted around the direct cur normal resonance frequency of the choke coil. rent source by shunting capacities C1. 'I'he lla-A 45 rNormally additional capacities areV placed in ments l, II and I5 of thermionic tubes 4, 6 and parallel with the tuning capacities thereby bring 8 respectively are connected through resistan'ees ing the capacity of all of the ganged condensers R to ground, thereby maintaining an operative to a value such that they track over the frebiasing potential between the control electrodes v quency range when used with tuning coils of 3, 9 and I3 and their respective'fllame'nts. Quiet 5U equal inductances. This did not result in satisoperation of the receiver is insured by the use of factory operation in some cases since the inductu an electrostatic screen S interposed betweenthe ance to capacity ratios of the several stages were inductances 2 and L. The inductances L, L1 and dissimilar, s L2 areeach tuned by a similar capacity C. As is v An object of this invention is `to. provide a Well known, it is desirable in practice to have all u of the tuning capacities C operated by a single control I5, as shown. It is present practice to mount said capacities on a single shaft.

In order to gang the condensers successfully it is necessary that the tune of the several circuits vary in proportion to the angular rotation of the ganged capacities. Since the inductances I are in parallel with the inductances L1, L2 the total effective inductance of the tuned circuits LiC and L2C is less than the effective inductance in the circuit LC if the inductances L, L1, L2 are of the same value and each capacity C of like value. For obvious reasons it is desirable that the condensers C for each stage be of substantially the same value, In order that the effective inductance in each of the tuned circuits LC, L1C, etc., be the same over the tuning range applicant makes the electrical values of inductances L1, Le larger than the inductance of L. In practice the effective choking inductance of I must be maintained suilicient so that the choke coil is resonant at a frequency above the range to be received on the receiver, so that the frequency of the signal received is below the natural resonance of the choke coil; then the choke coil will present an inductive reactance in parallel with the tuned coil.

Assuming that the effective choke coil inductance remains constant and the normal resonant frequency thereof is well above the frequency of operation of the receiver, the size of the inductances used in the various tuning circuits can be readily determined. For example, where inductance L is 1-1/10 microhenry and the choking inductances I to be used are 13 microhenry, then if inductances Li and L2 are made 1.20 microhenry, the resultant effective inductance of L1 and L2 in the tuned circuit when in parallel with the inductances I is in each case 1.10 microhenry. This practical application is given merely for purposes of illustration, and is not intended to limit the present invention since obviously the invention applies equally well to circuits to be used on wave bands other than the one of the example.

I claim:

, 1. A thermionic relay comprising a plurality of thermionic tubes each having anode, cathode and control electrode, means for applying alternating current potentials to said relay comprising an inductance connected between the control electrode and cathode of one of said tubes, means for connecting said tubes in cascade comprising an inductance connected between the anode and cathode of said tube, a third inductance of an inductive value greater than the inductive lvalue of said first named inductance, said third inductance being connected between the control electrode and cathode of another of said tubes, a capacity connecting the control electrode of said last named tube to the anode of said first named tube, tuning capacities of equal value connected in parallel with said first named inductance and with said last named inductance, and a common control for said tuning capacities.

2. Amplifying means comprising, a signal absorption member, a plurality of thermionic tubes, inductive means for applying potentials to be amplified to the input electrodes of one of said tubes, parallel inductances and a series capacity for coupling the output circuit of said tube to the input circuit of a succeeding tube, the effective inductance of said parallel inductances on the input circuit of said last named tube being made equal to the inductance in the input circuit of said first named tube, to permit tuning of said inductances by similar capacities, one or more variable capacities connected in parallel with said first named inductance, one or more variable capacities connected in parallel with one of said last named inductances, and single control means for said capacities.

3. A thermionic relay comprising, a plurality of thermionic tubes, each having a plurality of electrodes including control grid, cathode and anode, a tuned circuit including inductance and variable capacity connected between the control grid and cathode of one of said tubes for applying potentials to be relayed thereto, an inductance for applying charging potentials to the anode of said one of said tubes, a tuned circuit including an inductance and a variable capacity in parallel connected between the control grid and cathode of another of said tubes, said last named variable capacity being substantially equal in value to said first named variable capacity, and a coupling capacity connected between the control grid of. said last named tube and the anode of said rst one of said tubes, the inductance of said last named tuned circuit being greater than the inductance of said first named tuned circuit t0 compensate the effect of the inductance for applying charging potentials to the anode of said one of said tubes on said last named tuned circuit, whereby said variable capacities may be controlled as a unit to tune said relay to various frequencies within its range.

4. A radio relay including a plurality of tubes, a circuit including an inductance and a variable capacity connected between the control grid and cathode of the first of said tubes, circuits for connecting said tubes in cascade including, a separate inductance for charging the anode electrode of each of said tubes, a capacity connecting the anode of each of said tubes to the control grid of the following tube, and a circuit including an inductance and variable capacity equal in value to said first named variable capacity connected between the control grid and cathode of. said tubes following the rst, said last named inductance being of greater electrical value than said first named inductance to compensate the effect of said second named inductance on said second named tuned circuit, whereby said capacities may be controlled as a unit.

5. A radio relay as recited in claim 4 in which said second named inductance is normally resonant at a frequency slightly above the highest frequency to be relayed.

6. A thermionic relay comprising, a plurality of thermionic tubes, each having anode, cathode and control grid electrodes, means for applying alternating current potentials to be relayed to saidl relay comprising a tuned inductance connected between the grid and cathode of one of said tubes, an inductance connected between the anode and cathode of said one of said tubes, said inductance being resonant at a frequency above the frequency to which said rst named inductance is to be tuned, whereby said inductance presents an inductive reactance to said alternating current to be relayed, and means for connecting said tubes in cascade comprising, a capacity connecting the anode of said one tube to the control grid electrode of another of said tubes, a third inductance connected between the control grid and cathode of said last named tube, said third inductance having an inductive value greater than the inductive value of said first named inductance to compensate the parallel effect of said second and third inductance, whereby said first and third inductance may be tuned by similar capacities operated by a single control.

7. In an amplifier circuit, at least two electron discharge devices connected in cascade, each of. said devices being provided with anode, cathode and grid electrodes, an inductance coil connected between the grid and cathode of the first of said devices, a variable tuning condenser connected across said coil, a source of space current, means including an inductance coil for connecting the anode of said device to said source, a circuit including a capacity for connecting the anode of the rst device to a grid of the second device, a

tuned input circuit for the second device com-r prising a connection including an inductance f coil between the cathode and said grid electrode `discharge devices connected in cascade each of said devices being provided with anode, cathode and grid electrodes, a tuned input circuit for the first of said devices comprising a connection including an inductance coil between a grid and cathode thereof, a variable tuning condenser connected across said coil to tune the input circuit to any frequency within a predetermined range of. frequencies, a source of space current, means including an inductance coil for connecting the anode of said device to said source, a circuit including a capacity for connecting the anode of the iirst device to a grid of the second device, a tuned input circuit for the second device comprising a connection including an inductance coil between the cathode and said grid electrode thereof and a variable tuning condenser similar to the rst named tuning condenser connected across the last named inductance coil and arranged so as to tune the input circuit of the second device to any frequency within said band of frequencies, uni-control means for said variable condensers for tuning said input circuits simultaneously, said last named inductance coil having a different value of inductance than the first named inductance coil to compensate for the effect af the second named inductance coil upon the tuned input circuit of the second device and an output load connected between the anode and cathode of the second device.

BER'IRAM TREVOR. 

